This invention relates to a semiconductor diode optical amplifier, optical switch and optical modulator arrays within monolithic semiconductor structures and, more particularly, to combining angled facets with passive waveguides to decrease reflectivity of input and output facets and/or decrease the angle of those facets in angled arrays of optical amplifiers, optical switches, or optical modulators.
Semiconductor optical amplifiers are of interest for increasing the level of weak optical signals in fiber optic communications systems, for multiple electrode optical switches used to route signals in optical communication systems, for line-printing elements in advanced xerographic printers, and potentially as modulators for high-speed coding of information.
One of the most stringent requirements for operation of a semiconductor optical amplifier is suppression of internal optical reflections from the input and output facets of the semiconductor structure.
Semiconductor optical amplifiers require facets with exceptionally low internal reflectivity in order to suppress the onset of laser operation and thereby provide optical gain levels greater than those required to achieve lasing. Previously, reported work with optical amplifiers has achieved about 0.01% reflectivity by combining anti-reflective coatings on the facets, angling the amplification waveguide with respect to the facets, and flaring the amplification waveguide near the facet. However, this degree of suppression required the amplification waveguide to be inclined at 7 degrees to the facet normal. Inclination of the waveguide at such large angles with respect to the normal makes input and output coupling cumbersome and inefficient and leads to crescent shaped output profiles, known in the art as coma.
The flared ends of an amplification waveguide coupled to a facet are susceptible to conversion of single mode lasing to multiple mode outputs. Also, flared ends to amplification waveguides are difficult to fabricate within a closely spaced monolithic semiconductor structure array of amplifiers and other optical devices.
It is an object of this invention to provide an improved means for suppressing internal optical reflection at the input and output facets of a semiconductor optical amplifier.
It is another object of this invention to provide a means of reducing the angle to the input and output facets of a semiconductor optical amplifier array while still suppressing optical reflection at the facet.
It is another object of this invention to provide nonflared waveguides coupled to the input and output facet of a semiconductor optically amplifying array while still suppressing optical reflection at the facet.
It is yet another object of this invention to provide a means for suppressing internal optical reflection at the input and output facets of a semiconductor structure optical switching array.